The present invention relates to a system and method for rapid weighing of items. More particularly it relates to scales or weighing systems used in postage metering systems used to weigh and determine postage for mail pieces or the like.
Postal scale systems are well known. Such scale systems weigh a mail piece and determine the appropriate postage for that mail piece as a function of the weight. Postal mailing systems where a mail piece is transported onto a postage scale system, the appropriate postage is determined, and the mail piece is then transported to postage metering system for imprinting with a postal indicium representative of the postage determined are also known. One such system is described in U.S. Pat. No. 4,742,878; issued May 10, 1988. In such systems there is a constant need to increase the rate at which the scale can determine the weight of a mail piece in order that the throughput of the system can be increased.
U.S. Pat. No. 4,787,048; issued: Nov. 22, 1988, discloses one approach to decreasing the time required for a postage scale system to determine the weight of a mail piece. The system disclosed in this patent takes advantage of the structure of postage rate charts, i.e., the function that relates the weight of the mail piece to the appropriate postage amount. Such rate charts provide a constant postage value for all weights between a pair of predetermined weight breaks. The system of the ""048 patent takes advantage of this by use of an algorithm where a first estimate of the weight is made and used to determine the postage amount unless the first estimate is within a predetermined distance of a break point, in which case a second more accurate estimate is made.
While such systems have proven to be highly satisfactory for their intended purpose a basic problem remains that the weight of each mail piece in batches of mixed weight mail must be determined and the corresponding postage amount calculated before the vault (i.e. secure accounting registers which track postage expended by the meter to assure that the postal service receives payment for all mail pieces metered) can be debited for the postage amount and an appropriate indicium generated.
Thus it is an object of the present invention to provide a method and system for increasing the rate at which items such as mail pieces can be weighed and the time available to generate indicia and account for postage expended.
The above object is achieved and the disadvantages of the prior art are overcome in accordance with the present invention by a method and system including a transport assembly, the transport assembly having a transport for receiving and outputting mail pieces to be weighed, and for supporting the mail pieces during weighing and a feeder for successively feeding the mail pieces to the transport. A transducer mechanism supports the transport and generates an output representative of the load presented by the transport, from which the weight of mail pieces on the transport can be determined. In accordance with the method of the present invention a controller controls operation of the postage metering system so that after weighing of a current mail piece and a previous mail piece together, the transport is energized to advance the current mail piece and the previous mail piece, and a weight MW for the current mail piece is determined as the difference between a total weight TW on the transport and a weight PW for the previous mail piece. The feeder is then energized to input a next mail piece to the transport, and the transport is stopped so that the next mail piece and the current mail piece are supported by the transport for weighing together and the previous mail piece is output.
In accordance with one aspect of the present invention the controller generates an estimate, CE, of cumulative weighing error for the current mail piece as a function of a number of mail pieces weighed in a cycle of error accumulation and, if CE exceeds a predetermined limit, subsequently weighs a single mail piece separately to reinitialize the cycle of error accumulation.
In accordance with another aspect of the present invention the cycle is reinitialized if a weight interval, (MWxe2x88x92CE, MW+CE), intersects a weight interval (BPxe2x88x92O, BP+O), where BP is a rate break point in a predetermined postal rate schedule, and O is a predetermined offset.
In accordance with another aspect of the present invention CE is computed as (n+1)*E, where n+1 is the number of mail pieces weighed in the cycle of error accumulation and E is a maximum error in weighing one of the mail pieces.
In accordance with still another aspect of the present invention CE is computed as xcex1"sgr"e (n+1)1/2, where n+1 is the number of mail pieces weighed in the cycle of error accumulation, "sgr"e is a standard deviation of error e in weighing one of the mail pieces, and xcex1 is a predetermined constant.
In accordance with still another aspect of the present invention the mail pieces are printed with a postal indicium as they are transported by the transport.
In accordance with still another aspect of the present invention the controller generates a signal representative of a position of the transport for synchronizing printing of the indicium with movement of the mail piece.
In accordance with still another aspect of the present invention a print registration plate for aligning the mail pieces during printing is mounted on the transport.
Other objects and advantages of the present invention will be apparent to those skilled in the art from consideration of the detailed description set forth below and the attached drawings.